Study On Die-drawn Polypropylene/inorganic Particle Composites And The Strengthening Mechanism

Polypropylene（PP）resin has become one of the polymer materials consumed in modern society due to its advantages of high output,low cost,corrosion resistance,and easy processing.It is widely used in various fields such as commodities,packaging,vehicles,decoration,and medical treatment.At present,polypropylene materials produced in industry are mainly prepared by traditional melting methods,the crystal structure of the molded products is dominated by spherulites,with low mechanical strength and limited application scenarios.The main method to improve the properties of polypropylene materials is to composite with other reinforcing materials such as fibers,rigid particles,etc.,but the mechanical properties of polypropylene composites prepared by blending are still limited,and new methods and new technologies that can significantly improve the comprehensive mechanical properties of materials are urgently needed.In the process of processing,effectively maintaining the formed high-performance aggregated structure is the key to the enhancement and modification of polymers.As a kind of method to change the aggregation state of polymer materials to form microfiber crystal structure,solid-state molding can significantly improve the comprehensive properties of polymer materials.This project is based on inorganic particles calcium carbonate（Ca CO₃）filled modified polypropylene resin,which is applied to die drawing molding for solid secondary molding,and the aggregation of polypropylene composite materials is realized by using an external tensile force field.Based on the self-built die tensile experimental platform,light-weight,high-strength and high-modulus PP/Ca CO₃ composites with excellent mechanical properties were successfully prepared,The micro-structures,thermal properties,density and mechanical properties of polypropylene composites under different material parameters and process parameters were analyzed,and the structural evolution process and performance enhancement mechanism of the composite material during the die drawing process were explored.The main research work is as follows:1.A composite product containing three particle sizes of light Ca CO₃ with a filling amount of 30 wt%was prepared by die drawing method,and the effect of filler particle size on the performance of the product was explored,the best comprehensive performance of the product was selected.The optimum particle size parameter is 1250 mesh,and the prepared die-drawn composite material has the best comprehensive properties,with a tensile strength of 112.9 MPa,a flexural modulus of 5.05 GPa and a density of 0.87 g/cm³.2.Based on the influence of the particle size of filler Ca CO₃ on the properties of die-stretched products,the self-developed convergent die was used to prepare heavy Ca CO₃ composite products containing 30 wt%filling under different stretching ratio conditions.The tensile strength of die-stretched products is as high as 142.5 MPa,the flexural modulus is as high as 8.2 GPa,and the density is only 0.91 g/cm³.3.By sampling and marking samples at different positions in the mold,the crystal structure,thermal properties,microscopic morphology and density of the samples at different positions were characterized,and it was revealed that the molecular chain of the composite material was straightened and oriented during the die drawing process,and the crystal structure occurred.The evolution process of broke-up,slip,alignment and re-crystallization,crystal size refinement,crystallinity improvement and the formation process of micro-voids were analyzed.